Optimizing Carbon Coating Process for Lithium-Rich LiFePO₄ Cathode Materials

Graphical Abstract

This study investigates the effect of carbon coating sequence on the crystal structure and electrochemical performance of Li_1+xFe_1-XPO₄ (Li-rich LFP). Two approaches were compared: carbon coating before (C/BLF) and after (C/ALF) LFP crystal structure formation. The C/ALF process produced a dense carbon layer, reducing overpotential, underscoring the importance of process for improved material performance.

Abstract

Li_1+xFe_1-xPO₄ (Li-rich LFP) has been proposed as an alternative to address low ionic and electronic conductivity of stoichiometric LiFePO₄ (LFP). However, comprehensive studies investigating the impact of the carbon coating process on crystal structure and electrochemical performance during the synthesis of Li-rich LFP are still lacking. In particular, the characteristics of carbon precursor and calcination atmosphere significantly influence formation of crystal structure and electrochemical properties of the Li-rich LFP, underlining the necessity for further investigation. In this study, we compare two synthesis process: introducing carbon precursor before formation of LFP crystal structure (C/BLF) and adding it an additional calcination step after structure has formed (C/ALF). The C/ALF process sample has a larger unit cell volume and denser coating layer. As a result, the C/ALF sample exhibits a lower overpotential (0.54 V) and a higher discharge capacity (~134.13 mAhg⁻¹) than C/BLF sample. These findings elucidate the influence of carbon coating process sequence on crystal structure and electrochemical performance during the synthesis of Li-rich LFP.